How to... define monitors (report definitions) in Ansys Fluent

 There is often a situation when, after completing the analysis and obtaining a satisfactory level of partial equations, we may be unpleasantly surprised when we for example plot the  temperature in the RESULTS module. 

Example of monitor in Fluent

It may happen that the partial equations have an acceptable value, while the temperature in the solid domain or in the gas domain fluctuates (specially in static analyzes). This is disturbing information for us because it tells us that our analysis did not enter the typical steady state. Also in the case of transient analyzes, it may turn out that after plotting the desired variable, it may reach non-physical values. For example, when we plot the speed in a bottleneck, it may happen that it will have values of very large orders, which will not be in line with our intuition and engineering experience.

Therefore, in order to avoid such situations, it is extremely important to plot monitors for each analysis that verify the correctness of our assumptions. Monitors is the general name (more commonly found in the CFX program) of variables that we define in the model zones that interest us the most. At Fluent, we can define them in a function called Report Definitions.

Below I will present the steps that you need to follow to define Monitors.

Window where U can define monitor (report definitions ) in Fluent 

The first thing you need to do is double-click Report Definitions (red frame). Then, when the window appears, select the NEW option. A function block will develop where we can choose between different types of monitors. You can define a user function (Expresssion) exactly personalized to our requirements. You can also generate a monitor that tracks a given value on a given model plane or the volume of a given fragment (or the entire model). In today's post I will discuss the Volume Report which applies to most modeling cases in Fluent.

Volume Average Definition in Fluent 

After clicking on the Volume Report option, you can choose the most popular mathematical functions related to the analysis of a given volume. In our case, we click on the Volume-Average function which will monitor the average value of the volume that we will indicate in the next option. After confirming the option described above, we will have to choose which volume we will analyze in the monitor (pink frame). By default, this window includes the domains that we defined at the level of finite element mesh generation. Of course, in Meshing you can define subdomains that are volume regions contained in given model elements.

Of course, from the level of this window it is possible to change to a different type of monitor (first position in the green frame). In Field Variable, we choose the variable that we want to analyze, e.g. gas velocity, solid body temperature, wall heat transfer coefficient for -domains contact (of course, in this case, we should choose Surface Report).

In the gray frame, we should select all three options to properly archive our data from monitors (Report File, Report Plot, Print to Console). Finally, we should name our monitor (black frame). We clicked OK and that's all we had to do to define our monitor.

As you can see, defining monitors does not require a lot of work. Thanks to this feature, we can track many more factors while running a simulation. We have more control over the monitoring of our analysis, which will reduce the risk of making a serious error during modeling. The stage of definition of monitors should be constantly carried out during each of our subsequent numerical analyzes.

 In the next posts I will try to introduce other types of monitors, including user-defined (Expressions). Of course, I will also dont miss the definition of monitors in Ansys CFX. The path to be followed in this program is slightly different.

How to assign domain in Fluent  - report definitions